The purpose of this study is to characterize patterns of expression of the TGF-Betas in avian species and compare them to that in mammalian species. Towards this end, we have cloned and sequenced 4 avian TGF-Beta isoforms called TGF-Beta's 1, 2, 3, and 4. TGF-Beta's 1, 2, and 3 are related to their respective mammalian counterparts, while TGF-Beta 4 appears to be unique to the chicken. Using both Northern blot analysis to monitor mRNA expression as well as specific immunohistochemical reagents to detect expression of the different TGF-Beta isoforms, a complex pattern of expression of the various isoforms has been detected. In particular, it appears as if TGF-Beta 3 is expressed far more prominently in the chicken than in rodents. Moreover, expression of the TGF-Beta isoforms in chicken embryo chondrocytes, myocytes, and fibroblasts is differentially regulated by a variety of treatments including other growth factors, such as platelet-derived growth factor and interleukin-1, and by differentiating agents such as phorbol esters, dexamethasone, and retinoic acid. Recently, the promoter for chicken TGF-Beta 3 has been cloned and characterized in an attempt to understand the molecular basis underlying the differential expression patterns of this TGF-Beta isoform in rodents compared to chickens.